Radio-frequency particle separator



Oct. 11, 1966 V G. A. LOEW RADIO-FREQUENCY PARTICLE SEPARATOR Filed Dec.20, 1963 POWER SOURCE 3O UTILZATION DEVICE |O PARTICLE SEPARATOR VCOUPLER DEVICE TUBE ACCELERATOR TARGET INVENTOR GREGORY A. L05 wATTORNEY United States Patent Atomic Energy Commission Filed Dec. 20,1963, Ser. No. 332,318 2 Claims. (Cl. 250--41.9)

The present invention relates to a radio-frequency particle separatorcapable of physically separating high energy charged particles such aselectrons, protons, pi mesons, etc., moving at slightly differentvelocities in a charged particle beam. The invention is generallyutilized in conjunction with a bubble chamber or counter and is disposedto accept a particle beam generated by bombarding a target with, forexample, a beam accelerated by a linear accelerator. The resultingdesired portion of the particle beam emerging from the invention is thusavailable for further physics research.

Various devices are presently available for providing the desiredseparation of particles in a high energy beam having energies greaterthan, for example, 1 billion electron volts (BEV). Such devices includefor example, electrostatic separators, standing wave cavity separators,and traveling wave separators using various slow wave structures.

The present invention provides an extremely simple and straightforwardstructure which exhibits stronger defecting properties for a givenamount of radio-frequency in put power than do the above-mentioneddevices. When dealing with particle beam energies of the order of, forexample, 20 BEV and higher, such efliciency in the use of input power tothe separator is extremely advantageous.

The invention utilizes generally a cylindrical, periodically disk-loadedWaveguide with nonconcentric apertures formed in the disks through whichthe charged particles to be separated are made to drift. Unlike magneticparticle separators the invention causes a deflection of- Wanted andunwanted particles in accordance with the difference in their velocitiesand their entrance phase and not due to the difference of momenta. Theelectromagnetic wave which is propagated through the guide is of the TMtype. The transverse deflecting property of the device is caused not bythe choice of the TM mode of propagation as. in conventionalradio-frequemcy separators, but by off-centering the disk apertures,

and causing the propagation of radio-frequency energy in the separatorin the same basic mode as used in a related linear electron acceleratortube. The transverse deflecting property of the device is caused by theasymmetry obtained by off-centering the disk aperture. Thus, theparticle separator of the present invention by means of its constructionand related mode of electromagnetic wave propogation exerts atransversely deflecting force on charged particles synchronized with thepropagated wave. Hence, if microwave power is made to propagate alongsuch structure, particles which are synchronized with the wave at thecorrect phase will undergo a cumulative transverse deflection whereasparticles traveling at a dif ferent velocity will, on the average,undergo no deflection. With a bunched beam and a short structure, ifparticles of different velocities are caused to drift with respect toeach other by half a wavelength prior to their injection into theseparator, they will be deflected in diverging directions and thereby bephysically separated into two distinct beams.

Accordingly it is an object of the present invention to provide a simpledevice capable of separating particles in a very high energy particlebeam at a particular frequency, wherein the particles are moving atslightly different velocities.

It is another object of the present invention to provide a particlese'parartor which utilizes a TM type mode propagated therein to realizethe desired deflection of particles passing therethrough.

It is still another object of the present invention to provide atravelling wave particle separating device of relatively high shuntimpedance and a corresponding, inherent, high deflecting efficiency.

Yet another object of the present invention is to provide aradio-frequency particle separator wherein the transverse deflectingproperty of the device is provided by cit-centering the disk aperturesand causing the propagation of radio-frequency energy therein in the TMmode which is the same mode as that in the accelerator tube.

Another object of the present invention is to provide a radio-frequencyparticle separator which reduces the possibility of mode rotation in thestructure, which rotation generally exists in separators using the TMmode, wherein the reduction is due to the inherent asymmetry of thestructure of the device.

Other objects and advantages will be apparent in the followingdescription and claims considered together with the accompanyingdrawing, in which:

FIGURE 1a is a perspective partially broken-out schematic view of theradio-frequency patricle separator of the present invention.

FIGURE 1b is a graph of the electric field generated within theseparator of FIGURE 1a as a function of the radial distance along a linedefined by the central axes of a disk and its aperture.

FIGURE 2 is a block diagram of a portion of an accelerator system inwhich known elements are shown combined with the particle separator ofthe present invention.

Referring more particularly to the drawing, there is shown aradio-frequency particle separator 10 in accordance with the presentinvention, comprising substantially a cylindrical disk-loaded waveguide.More particularly, an elongated cylindrical waveguide 12 having aninside radius b and a centrally extending geometrical axis lying alongthe z-coordinate, has disposed concentrically within and along thelength thereof a series of equally spaced disks 14. Each of disks 14 hasan aperture 16 formed therein in nonconcentric relation to thecylindrical waveguide 12. That is, apertures 16 in disks 14 are disposedin off-axis relation to the centrally extending geometrical axis of thewaveguide 12. Apertures 16, however, are arranged in alignment along acommon longitudinal axis thereof which axis is parallel to and spacedfrom the axis of waveguide 12. Thus, a particle beam 18 containing highenergy charged particles moving at different velocities, and which isgenerated by bombarding a target with a suitable high energy particlebeam, is injected into the separator 10 along the apertures 16 therein.Such beam 18 is separated into the desired number or configurations ofdistinct beams, e.g., 20, 22 and 24. If the apertures 16 are disposedoff-axis in a horizontal direction with respect to the axis of theWaveguide 12, as shown in FIG. 1a, then the direction of deflection ofthe emerging beams 20, 22 and 24 is along the same horizontal plane.

In operation, an electromagnetic wave of the TM type is supplied to thecylindrical waveguide 12 from an exterior radio-frequency power source30 (FIGURE 2) by means of a suitable coupler device 31 which iscoaxially secured at the input end of the separator. The coupler is, inessence, a cavity of suitable dimensions and operates to convert theincoming radio-frequency power from the TE mode of the rectangularwaveguide to the TM mode of the circular separator. Since coupling ofpower to waveguides by means of couplers is known standard practice, nofurther discussion thereof is believed necessary. The transversedeflecting property of the separator 10 is supplied not by the TM modepropagated through the guide as in most traveling wave separators, butby the asymmetry of the propagating field which in turn, is obtained byoff-centering the disk apertures 16 in accordance with the invention.The longitudinal electric field E along the z or axial direction, whichwould normally be constant over the respective disk apertures if samewere centered along the axis of the waveguides 12, is seen in FIGURE 1bto undergo a variation as a function of the distance across the disks.The phase shift per cavity defined between successive disks 14, andhence, the phase velocity of the wave propagated therein at the givenfrequency, may be determined by the choice of the axially extendingdistance d between disks 14 and the inside radius b of the cylindricalwaveguide 12. A typical applicable phase shift is 1r/2 or 21r/3 percavity. The cross sectional dimensions, a and b, of the device aredetermined by the choice of the frequency of the microwave power sourceto be used. Thus, in accordance with the invention, the apertured disksare spaced apart a distance substantially equal to XO/n, where A is thefree space wavelength, and n is the desired number of disks perwavelength. Further, the inside diameter of the cylindrical waveguide12, i.e., the outside diameter of the disks 14 is approximately equal toAO/ 1.305, the diameters of the apertures 16 are approximately equal tokO/S, and are formed in the disks 14 with their respective centersdisposed a distance approximately equal to AO/S from the axis of thecylindrical waveguide 12 and along a common axis. The length and numberof cavities of the device depends on the energy of the particles to beseparated, the desired angle of separation and the magnitude of theavailable microwave power. A typical power source for introducing thedesired driving radiofrequency power to the separator by way of thecoupler would be a high power klystron.

While the invention has been disclosed herein with respect to a singlepreferred embodiment, it will be apparent to those skilled in the artthat numerous modifications and variations are possible within thespirit and scope of the invention, and thus it is not intended to limitthe invention except by the terms of the following claims.

What is claimed is:

1. A particle separator for separating high-energy particles havingdifferent velocities, comprising:

(a) a radio-frequency power source for generating electromagnetic wavesof a preselected frequency;

(b) a cylindrical waveguide, the inner diameter of said waveguide beingsubstantially equal to Ml/ 1.305, Where A0 is the free space wavelengthof said electromagnetic waves;

(c) means for coupling said radio-frequency power source to saidcylindrical waveguide in the TM mode; and

(d) a plurality of disks concentrically mounted within said waveguide,said disks being spaced apart a distance substantially equal to AO/n,where n is the desired number of disks per wavelength of saidelectromagnetic wave, said disks having apertures of a diametersubstantially equal to AO/S, which apertures are aligned along an axiswhich is disposed substantially AO/S from the axis of said waveguide.

2. A particle separator according to claim 1, further including meansfor generating a high-energy particle beam, 2. target in the path of thebeam upon which the beam impinges to generate a high-energy secondarybeam which includes charged particles of at least two differentvelocities, said target being arranged to direct said secondary beamthrough said coupling means to enter along the axis of said apertures,and wherein said coupling means is of a length causing the particles ofdifferent velocities in the secondary beam to spatially separatetherealong by approximately half a wavelength of the electromagneticwaves generated by said source.

References Cited by the Examiner UNITED STATES PATENTS 2,818,507 12/1957Britten 25041.9 2,911,532 11/1959 Tipotsch 250-4l.9 3,093,733 6/1963Blewe'tt et al 250-419 RALPH G. NILSON, Primary Examiner.

W. F. LINDQUIST, Assistant Examiner.

1. A PARTICLE SEPARATOR FOR SEPARATING HIGH-ENERGY PARTICLES HAVINGDIFFERENT VELOCITIES, COMPRISING: (A) A RADIO-FREQUENCY POWER SOURCE FORGENERATING ELECTROMAGNETIC WAVES OF A PRESELECTED FREQUENCY; (B) ACYLINDRICAL WAVEGUIDE, THE INNER DIAMETER OF SAID WAVEGUIDE BEINGSUBSTANTIALLY EQUAL TO $0/1.305, WHERE $0 IS THE FREE SPACE WAVELENGTHOF SAID ELECTROMAGNETIC WAVES; (C) MEANS FOR COUPLING SAIDRADIO-FREQUENCY POWER SOURCE TO SAID CYLINDRICAL WAVEGUIDE IN THE TM01MODE; AND (D) A PLURALITY OF DISKS CONCENTRICALLY MOUNTED WITHIN SAIDWAVEGUIDE, SAID DISKS BEING SPACED APART A DISTANCE SUBSTANTIALLY EQUALTO $0/N, WHERE N IS THE DESIRED NUMBER OF DISKS PER WAVELENGTH OF SAIDELEC-